In a method known from Japanese Patent 62-59539, a glass parison is heated in an oven by thermal radiation energy until a portion of the glass parison has a desired viscosity. The glass is then moulded into the desired shaped. The thermal radiation energy is derived from a halogen lamp.
A disadvantage of this known method is that the time which elapses before a portion of the glass parison has the desired viscosity is comparatively long. Moreover, the radiation energy also heats the mould. The mould will expand as a result and assume a different shape. The dimensions of products manufactured with these moulds are accordingly dependent on the shape of the moulds at the increased temperature which is indeed insufficiently controllable.
In the case of precision moulding of optical products, for example lenses for use in LCD players, high requirements are imposed on the dimensions of the moulded lenses, and it is undesirable for the dimensions of the lenses to be determined by the dimensions of the moulds at the said insufficiently controllable temperature.